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Envoy CVE-2026-26308

HIGH
Incorrect Authorization (CWE-863)
2026-03-10 security-advisories@github.com GHSA-ghc4-35x6-crw5
Authentication Bypass Envoy
7.5
CVSS 3.1 · GitHub Advisory
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Severity by source

GitHub Advisory PRIMARY
7.5 HIGH
AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
None

Lifecycle Timeline

4
Analysis Generated
Mar 12, 2026 - 21:55 vuln.today
PoC Detected
Mar 11, 2026 - 16:23 vuln.today
Public exploit code
Patch released
Mar 11, 2026 - 16:23 nvd
Patch available
CVE Published
Mar 10, 2026 - 20:16 nvd
HIGH 7.5

DescriptionGitHub Advisory

Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, the Envoy RBAC (Role-Based Access Control) filter contains a logic vulnerability in how it validates HTTP headers when multiple values are present for the same header name. Instead of validating each header value individually, Envoy concatenates all values into a single comma-separated string. This behavior allows attackers to bypass RBAC policies-specifically "Deny" rules-by sending duplicate headers, effectively obscuring the malicious value from exact-match mechanisms. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.

AnalysisAI

Envoy's RBAC filter improperly concatenates duplicate HTTP headers into comma-separated strings instead of validating each value individually, allowing attackers to bypass "Deny" access control policies through header manipulation. This vulnerability affects Envoy versions prior to 1.34.13, 1.35.8, 1.36.5, and 1.37.1, and public exploit code exists. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Send HTTP request with duplicate headers
Exploit
Envoy concatenates values into comma-separated string
Execution
RBAC Deny rule bypassed via obscured value
Impact
Access unauthorized resource
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Vulnerability AssessmentAI

Exploitation Envoy proxy version prior to 1.37.1, 1.36.5, 1.35.8, or 1.34.13 with RBAC filter enabled and Deny rules configured for HTTP header exact-match validation. Additional conditions and limiting factors are described in the full assessment.
Risk Assessment CVSS 7.5 (HIGH). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker could exploit this vulnerability to bypass RBAC policies—specifically "Deny" rules—by sending duplicate headers, eff.
Remediation A vendor patch is available — apply it immediately. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Inventory all Envoy deployments and verify affected versions (pre-1.37.1, pre-1.36.5, pre-1.35.8, pre-1.34.13). …

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CVE-2026-26308 vulnerability details – vuln.today
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